In many communication systems, binary data is communicated between transmitters and receivers in a serial manner, one bit at a time over a communication link, for example, over an electrical line.
In some systems, the method for transmitting data over the serial link requires that there be a limit on the number of consecutive equal values (e.g., runs of zero or runs of one).
In some systems, the serial data is divided into sections, often referred to as frames, and the signal transmitted on the link includes markers identifying or separating the frames.